Section 14D. The agreement made under section fourteen B, or any amendment to such an agreement, may provide that the incurring of indebtedness by the district shall be approved by the registered voters in the member towns pursuant to the provisions of clause (n) of section sixteen. In any district for which the agreement does not so provide, the incurring of indebtedness shall be subject to disapproval by any member town pursuant to the provisions of clause (d) of said section sixteen. Notwithstanding the provisions of this section, the regional district school may, by vote of two-thirds of all its members, require that the approval of any particular authorized issue of indebtedness shall be by the registered voters of the member towns of the district pursuant to the provisions of clause (n) of section sixteen rather than pursuant to the provisions of clause (d) of said section sixteen.